ELECTROMAGNETIC WAVES ABSORBING MATERIAL

Abstract

The present invention relates to an electromagnetic millimetre wave absorber material, preferably having a volume resistivity of more than 1 cm, containing solid particles having an aspect ratio (length:diameter) of at least 5 of a first electrically conductive material, particles having an aspect ratio (length:diameter) of less than 5 of a second electrically conductive material and an electrically non-conductive polymer, wherein the absorber material is preferably capable of absorbing electromagnetic waves in a frequency region of 60 GHz to 200 GHz and wherein the electromagnetic millimetre wave absorber material comprises based on the total amount of the absorber material from 30 wt.-% to 93 wt.-% of the electrically non-conductive polymer, from 6.5 wt.-% to 10 wt.-% of the first electrically conductive material, from 0.5 wt.-% to 0.9 wt.-% of the second electrically conductive material, and from 0 wt.-% to 59.1 wt.-% of one or more additives. The invention also relates to its use and method for absorbing as well as a sensor apparatus comprising said absorber material.

Claims

1. An electromagnetic millimetre wave absorber material containing solid particles having an aspect ratio (length:diameter) of at least 5 of a first electrically conductive material, particles having an aspect ratio (length:diameter) of less than 5 of a second electrically conductive material, and an electrically non-conductive polymer, wherein the electromagnetic millimetre wave absorber material comprises based on the total amount of the absorber material from 30 wt.-% to 93 wt.-% of the electrically non-conductive polymer, from 6.5 wt.-% to 10 wt.-% of the first electrically conductive material, from 0.5 wt.-% to 0.9 wt.-% of the second electrically conductive material, and from 0 wt.-% to 59.1 wt.-% of one or more additives.

2. The absorber material of claim 1, wherein the solid particles having the aspect ratio (length:diameter) of at least 5 of the first electrically conductive material are solid fibre particles having an acicular or cylindrical shape or a turned chip like shape.

3. The absorber material of claim 1, wherein the particles having the aspect ratio (length:diameter) of less than 5 of a second electrically conductive material are non-fibrous particles having a spherical or lamellar shape.

4. The absorber material of claim 1, wherein the electrically non-conductive polymer is a thermoplast, thermoplastic elastomer, thermoset, or a vitrimer.

5. The absorber material of claim 1, wherein the particles of the first and second electrically conductive material are homogenously distributed in the absorber material.

6. The absorber material of claim 1, wherein the absorber material is subject to injection molding, thermoforming, compression molding, or 3D printing.

7. The absorber material of claim 1, wherein the electromagnetic millimetre wave absorber material comprises based on the total amount of the absorber material from 40 wt.-% to 92.49 wt.-% of the electrically non-conductive polymer, from 7.0 wt.-% to 9.0 wt % of the first first electrically conductive material, from 0.51 wt.-% to 0.80 wt.-% of the second electrically conductive material, and from 0 wt.-% to 50.2 wt.-% of one or more additives.

8. The absorber material of claim 1, wherein the electromagnetic millimetre wave absorber material comprises based on the total amount of the absorber material from 50 wt.-% to 91.99 wt.-% of the electrically non-conductive polymer, from 7.5 wt.-% to 8.5 wt % of the first first electrically conductive material, from 0.51 wt.-% to 0.70 wt.-% of the second electrically conductive material and from 0 wt.-% to 40.8 wt.-% of one or more additives.

9. The absorber material of claim 1, wherein the first and second electrically conductive material is carbon or a metal.

10. The absorber material of claim 9, wherein the metal is zinc, nickel, copper, tin, cobalt, manganese, iron, magnesium, lead, chromium, bismuth, silver, gold, aluminum, titanium, palladium, platinum, tantalum, or an alloy thereof.

11. The absorber material of claim 1, wherein at least one of the following prerequisites is fulfilled: the first electrically conductive material is iron or steel and the second conductive material is carbon; the particles of the second electrically conductive material are carbon black; the iron or iron alloy material is stainless steel; the particles of the first electrically conductive material have a length of from 0.01 to 100 mm; the particles of the first electrically conductive material have a diameter of from 0.1 m to 100 m.

12. The absorber material of claim 1, wherein the one or more additives is selected from the group consisting of at least one electrically non-conductive filler, antioxidants, lubricants, nucleating agents, impact modifying polymers, or other processing aids.

13. An electronic device containing a radar absorber in form of a radar absorber part or a radar absorbing housing, the radar absorber comprising at least an absorber material of claim 1, wherein the at least one absorber material is comprised in the electronic device in the radar absorber; at least one transmission area, transmissible for electromagnetic millimeter waves in a frequency region of 60 GHz to 200 GHz; and a sensor capable of detecting and optionally emitting electromagnetic millimeter waves in a frequency region of 60 GHz to 200 GHz through the transmission area.

14. (canceled)

15. A method of absorbing electromagnetic millimeter waves in a frequency region of 60 GHz to 200 GHz, comprising irradiating an absorber material of claim 1 with electromagnetic millimeter waves in a frequency region of 60 GHz to 200 GHz.

16. The absorber material of claim 1 having a volume resistivity of more than 1 cm.

17. The absorber material of claim 1 capable of absorbing electromagnetic waves in a frequency region of 60 GHz to 200 GHz.

18. The absorber material of claim 9, wherein the first electrically conductive material is a metal and the second electrically conductive material is carbon.

19. The absorber material of claim 4, wherein the electrically non-conductive polymer is a thermoplastic material.

20. The absorber material of claim 19, wherein the thermoplastic material comprises a polyester.

21. The absorber material of claim 20, wherein the polyester comprises poly(butylene terephthalate).

Description

EXAMPLES

[0185] Materials

[0186] Poly(butylene terephthalate) (PBT, Ultradur B4500 NAT) were obtained from BASF SE. Black pearls 880 (aspect ratio<5) were obtained from Cabot corporation. The stainless-steel fiber (stainless steel 1.4113) with a broad length distribution including particles with aspect ratio>5) was obtained from Deutsche Metallfaserwerk.

[0187] Measurement of the Interaction with Electromagnetic Waves

[0188] The experimental setup for the characterization of the absorbers in the range 60-90 GHz is as follows.

[0189] A vectoral network analyzer Keysight N5222A (10 MHz-26.5 GHz), two Keysight T/R mm head modules N5256AW12, 60-90 GHz and as a sample holder a swissto12 corrugated waveguide WR12+, 55-90 GHz. The calibration of the corrugated waveguide (cw) is done by doing a thru and short measurement. For the thru measurements the flanges of the cw are connected, for the short measurement, a metal plate is inserted between the flanges. The field distribution of the cw is described in: IEEE Transactions on Microwave Theory and Techniques 58, 11 (2010), 2772.

[0190] After the calibration, the sample (minimum diameter 2 cm) is inserted between the flanges of the cw and the S11 (reflection) and S21 (transmission) parameters are measured in the range 60-90 GHz (amplitude and phase). From the measured S11 and S22 parameters, the absorption A of the sample was calculated as follows: A (%)=100S11(%)S21(%).

[0191] From the measured parameters, the dielectric parameters (dielectric permittivity) and (dielectric loss factor) of the sample material is calculated at each frequency point using the swissto12 materials measurement software.

[0192] In order to determine the absorption values at 0 and 90 the sample was measured twice in this set-up. Once the flow direction (i.e. orientation of the fibrous electrically conductive particles) from the injection molding of the sample was place parallel to the electric field (0) and once was the sample rotated by 90 to yield the orientation of the fibrous electrically conductive particles where the flow direction is perpendicular to the electric field (90). The absorption is the difference between the absorption in the two orientations.

[0193] Preparation of the Comparative Example C1 to C5 and Inventive Example E1

[0194] General procedure of the preparation of inventive and comparative examples Poly(butylene terephthalate) (PBT, Ultradur B4500 NAT) was obtained from BASF SE and dried to a water content below 0.04 wt %. The PBT, the lubricant and the carbon black batch were fed into to extruder (ZE25) with a barrel temperature of 270 C. and an output of 15 kg/h. Steel fibers were added directly in the melt in zone 4 of the extruder to prevent excessive shearing of the fibers. Material was granulated and dried to a water content below 0.04 wt %. The samples for the electromagnetic analysis (60601 mm) were injection molded using 260 C. for melt temperature, 60 C. for mold temperature. All examples were prepared using this approach.

[0195] The compositions of the inventive (E1) and comparative examples (C1-C5) are shown in Table 1.

TABLE-US-00002 TABLE 1 Compositions of the inventive (E1) and comparative examples (C1-C5). E1 C1 C2 C3 C4 C5 PBT resin (B4500 % 88.5 86.5 85.5 90.5 89.5 92.5 nat) (90.9)*.sup.) (90.5)*.sup.) (91.1)*.sup.) (92.1)*.sup.) (92.7)*.sup.) (93.3)*.sup.) Carbon black % 3 5 7 2 4 1 batch (20% car- (0.6)**.sup.) (1.0)**.sup.) (1.4)**.sup.) (0.4)**.sup.) (0.8)**.sup.) (0.2)**.sup.) bon black Black - Pearls 880 - in PBT) Lubricant (C16- % 0.5 0.5 0.5 0.5 0.5 0.5 C18 fatty esters of pentaerythritol) Stainless-steel % 8 8 7 7 6 6 fiber Absorption 0 dB 10.1 9.1 7.4 7.5 6.7 6.6 Absorption 90 dB 10.4 12.8 11.5 10.2 10.0 10.3 absorption dB 0.3 3.7 4.1 2.7 3.3 3.7 *.sup.)total PBT content including PBT from carbon black batch **.sup.)carbon black Black - Pearls 880 content from carbon black batch

[0196] From these results it is clear that inventive sample E1 has a good absorption with an unexpected low anisotropy even though it contains high amount of fibrous electrically conductive particles.